/*
 * Copyright (c) 2005, 2006, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */

package javax.lang.model.util;

import static javax.lang.model.SourceVersion.RELEASE_6;

import javax.annotation.processing.SupportedSourceVersion;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.Element;
import javax.lang.model.element.ExecutableElement;
import javax.lang.model.element.PackageElement;
import javax.lang.model.element.TypeElement;
import javax.lang.model.element.TypeParameterElement;
import javax.lang.model.element.VariableElement;

/**
 * A simple visitor of program elements with default behavior appropriate for
 * the {@link SourceVersion#RELEASE_6 RELEASE_6} source version.
 * 
 * Visit methods corresponding to {@code RELEASE_6} language constructs call
 * {@link #defaultAction}, passing their arguments to {@code defaultAction}'s
 * corresponding parameters.
 * 
 * <p>
 * Methods in this class may be overridden subject to their general contract.
 * Note that annotating methods in concrete subclasses with
 * {@link java.lang.Override @Override} will help ensure that methods are
 * overridden as intended.
 * 
 * <p>
 * <b>WARNING:</b> The {@code ElementVisitor} interface implemented by this
 * class may have methods added to it in the future to accommodate new,
 * currently unknown, language structures added to future versions of the
 * Java&trade; programming language. Therefore, methods whose names begin with
 * {@code "visit"} may be added to this class in the future; to avoid
 * incompatibilities, classes which extend this class should not declare any
 * instance methods with names beginning with {@code "visit"}.
 * 
 * <p>
 * When such a new visit method is added, the default implementation in this
 * class will be to call the {@link #visitUnknown visitUnknown} method. A new
 * simple element visitor class will also be introduced to correspond to the new
 * language level; this visitor will have different default behavior for the
 * visit method in question. When the new visitor is introduced, all or portions
 * of this visitor may be deprecated.
 * 
 * @param <R>
 *            the return type of this visitor's methods. Use {@code Void} for
 *            visitors that do not need to return results.
 * @param <P>
 *            the type of the additional parameter to this visitor's methods.
 *            Use {@code Void} for visitors that do not need an additional
 *            parameter.
 * 
 * @author Joseph D. Darcy
 * @author Scott Seligman
 * @author Peter von der Ah&eacute;
 * @since 1.6
 */
@SupportedSourceVersion(RELEASE_6)
public class SimpleElementVisitor6<R, P> extends AbstractElementVisitor6<R, P> {
	/**
	 * Default value to be returned; {@link #defaultAction defaultAction}
	 * returns this value unless the method is overridden.
	 */
	protected final R DEFAULT_VALUE;

	/**
	 * Constructor for concrete subclasses; uses {@code null} for the default
	 * value.
	 */
	protected SimpleElementVisitor6() {
		DEFAULT_VALUE = null;
	}

	/**
	 * Constructor for concrete subclasses; uses the argument for the default
	 * value.
	 * 
	 * @param defaultValue
	 *            the value to assign to {@link #DEFAULT_VALUE}
	 */
	protected SimpleElementVisitor6(R defaultValue) {
		DEFAULT_VALUE = defaultValue;
	}

	/**
	 * The default action for visit methods. The implementation in this class
	 * just returns {@link #DEFAULT_VALUE}; subclasses will commonly override
	 * this method.
	 * 
	 * @param e
	 *            the element to process
	 * @param p
	 *            a visitor-specified parameter
	 * @return {@code DEFAULT_VALUE} unless overridden
	 */
	protected R defaultAction(Element e, P p) {
		return DEFAULT_VALUE;
	}

	/**
	 * {@inheritDoc} This implementation calls {@code defaultAction}.
	 * 
	 * @param e
	 *            {@inheritDoc}
	 * @param p
	 *            {@inheritDoc}
	 * @return the result of {@code defaultAction}
	 */
	public R visitPackage(PackageElement e, P p) {
		return defaultAction(e, p);
	}

	/**
	 * {@inheritDoc} This implementation calls {@code defaultAction}.
	 * 
	 * @param e
	 *            {@inheritDoc}
	 * @param p
	 *            {@inheritDoc}
	 * @return the result of {@code defaultAction}
	 */
	public R visitType(TypeElement e, P p) {
		return defaultAction(e, p);
	}

	/**
	 * {@inheritDoc} This implementation calls {@code defaultAction}.
	 * 
	 * @param e
	 *            {@inheritDoc}
	 * @param p
	 *            {@inheritDoc}
	 * @return the result of {@code defaultAction}
	 */
	public R visitVariable(VariableElement e, P p) {
		return defaultAction(e, p);
	}

	/**
	 * {@inheritDoc} This implementation calls {@code defaultAction}.
	 * 
	 * @param e
	 *            {@inheritDoc}
	 * @param p
	 *            {@inheritDoc}
	 * @return the result of {@code defaultAction}
	 */
	public R visitExecutable(ExecutableElement e, P p) {
		return defaultAction(e, p);
	}

	/**
	 * {@inheritDoc} This implementation calls {@code defaultAction}.
	 * 
	 * @param e
	 *            {@inheritDoc}
	 * @param p
	 *            {@inheritDoc}
	 * @return the result of {@code defaultAction}
	 */
	public R visitTypeParameter(TypeParameterElement e, P p) {
		return defaultAction(e, p);
	}
}
